1. Field of the Invention
The present invention relates to a fuel injection control apparatus for controlling an amount of fuel supplied to an internal combustion engine for a motor vehicle or automobile or the like.
2. Description of the Related Art
In general, in the internal combustion engine (hereinafter also referred to simply as the engine) and in particular in the engine for a motor vehicle equipped with an exhaust gas purification system in which a tertiary catalytic converter (also known as the catalytic converter rhodium or CCRO in abbreviation) is employed, it is required to maintain the air-fuel ratio of an exhaust gas resulting from combustion of a fuel mixture within the engine cylinder (hereinafter this air-fuel ratio will be referred to as the exhaust gas air-fuel ratio for convenience of description) at a value very close to a stoichiometric air-fuel ratio. To this end, when the engine is in the acceleration state or mode, the amount of fuel injection determined on the basis of, for example, the rotation number (rpm) of the engine, a load imposed on the engine and other factors is increased by a proportion which corresponds to the acceleration, while when the engine is in the deceleration mode, the above-mentioned fuel amount is decreased by a proportion equivalent to the deceleration so that the optimal exhaust gas air-fuel ratio can be realized regardless of changes in the engine operation state.
In the fuel injection control apparatus for the engine system of the type mentioned above, it is necessary to detect the engine operation state, i.e., acceleration and deceleration states or modes of the engine. Under the circumstances, the acceleration and the deceleration of the engine are generally determined on the basis of the magnitude of change (or rate of change) in the outputs of an intake air flow sensor or a pressure sensor for detecting a pressure prevailing in an intake pipe, which outputs can typically represent the load of the engine, wherein the amount of fuel injection is increased or decreased in dependence on the change in the engine load. In that case, the output signals of the air flow sensor or the pressure sensor are inputted to the fuel injection control apparatus in the form of electric signals on the basis of which decision as to acceleration and deceleration is performed.
In the fuel injection control apparatus mentioned above, predetermined values defining a dead zone are previously set in consideration of influences of noise to the electric signals, wherein the decision concerning acceleration and deceleration is validated only when the magnitude of change in the electric signals made use of for determining the acceleration and deceleration deviates from the dead zone.
In conjunction with the fuel injection control apparatus for the engine which is implemented in such structure as described above, there naturally arises a demand for performing the decision as to acceleration and deceleration of the engine with a high accuracy because of necessity for holding the exhaust gas air-fuel ratio at a value at least approximating the stoichiometric air-fuel ratio in the acceleration and deceleration mode of the engine, which in turn requires that the width of the dead zone (or reference value range) be set as narrow as possible while taking into account a noise margin.
Further, the fuel injection control apparatus known heretofore suffers from a problem that when the engine operation is accelerated by depressing steeply the acceleration pedal to a depth corresponding to a predetermined opening degree of the throttle valve, there may take place overshoot in the output level of the air flow sensor and the pressure sensor, which will lead to an erroneous decision that the acceleration is erroneously taken as deceleration, making thus it impossible to maintain the exhaust gas air-fuel ratio close to the stoichiometric ratio, to a great disadvantage.
Besides, when the engine is decelerated, that is, when the acceleration pedal is released to such an extent that the throttle valve is fully closed, undershoot may take place in the output signal levels of both the intake air flow sensor and the pressure sensor, as a result of which a decision of engine acceleration is performed in spite of a deceleration state, so that the exhaust gas air-fuel ratio can not be maintained at a value close to the stoichiometric ratio, giving rise to another problem.